Celtic have signed Derk Boerrigter from Ajax on a four-year deal subject to international clearance for an undisclosed fee believed, according to sources in the Netherlands, to be about £3m.

The 26-year-old forward completed his medical in Glasgow on Tuesday and becomes Neil Lennon's fourth recruit of the summer following the acquisitions of Amido Baldé, Virgil van Dijk and Steven Mouyokolo.

The Celtic manager said Boerrigter would go straight into the squad for the Champions League third qualifier against the Swedish side Elfsborg at Parkhead on Wednesday night.

Celtic have not disclosed the fee for the former RKC Waalwijk and PEC Zwolle player but reports in the Netherlands are suggesting that a figure of £3m would have been required to persuade Ajax to part with the winger.

Boerrigter made 30 appearances for Ajax last season in his second spell at the club, which included 13 as a substitute, and scored five goals.

He began his professional career at the Amsterdam-based side in 2005 when he signed a two-year contract. However, Boerrigter played only for the youth team and, although he started on the bench in several first-team games, he never made his full debut.

The winger rejoined the current Eredivisie champions in 2011 after a loan spell at the now defunct HFC Haarlem and two seasons apiece at Zwolle and RKC and scored for his side in the 4-1 Champions League defeat by Real Madrid last season.